Traffic cycle offset selectors



Dec. 20, 1966 G. D. HENDRICKS TRAFFIC CYCLE OFFSET SELECTORS 4 Sheets-Sheet 1 .rST

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G; DONALD H ENDRICKS ATTQRNEY Dec. 20, 1966 Original Filed Oct. 20, 1958 G. D. HENDRICKS TRAFFIC CYCLE OFFSET SELECTORS 4 Sheets-Sheet 2 OFFSET VOLTA E RATI c N l f DIVID Rs DETECIQORS CIRCUIT INBOUND 62 GREATER v02 R02 6 maouwo 7 HIGHER LE5$ER l CATHODE BALANCE 1 IC'FOLLQWER DETECTOR D AMPLIFIER BD CFA j OUTBOUND 63 g 31$ LOWER LESSER I CIRCUIT vns R03 SR ouraoum: F G 5 GREATER Q ISO \SIMULTANEOUS OPERATION CONTROL ClRCUIT GREATER Wino VOLTAGE DETECTOR 62 I 2 DIVIDER 7 H'GHER LESSER RATIO 6 i ifi CATHODE BALANCE @Hggg DETECTOR CIRCUIT IC- FOLLOWER DETECTOR SR AMPLIFIER 50 VD] H Rm oo- 2 CFA a LowER ISO 65 SIMULTANEOUS OPERATION INVENTOR.

G. DONALD HENDRICKS ATTORNEY 4 SheetsSheet 3 G. D. HENDRICKS TRAFFIC CYCLE OFFSET SELECTORS Original Filed Oct. 20, 1958 Dec. 20, 1966 Dec. 20, 1966 s. D. HENDRICKS 3,293,601

TRAFFIC CYCLE OFFSET SELECTORS Original Filed Oct. 20, 1958 4 Sheets-Sheet 4 INVENTOR.

G. DONALD HENDRICKS BY [3% ATTORNEY United States Patent 13 Claims. (Cl. 34035) This invention relates to improvement in the method of selecting one of a number of traffic cycle offsets according to relative trafiic density on a thoroughfare. The invention also relates to improvement in apparatus therefor. The apparatus is flexible and may be set up to provide at least two offset plans, preferential and nonpreferential.

This application is a continuation of my co-pending application, Serial No. 768,193, filed October 20, 1958, which is in turn a continuation-in-part of my then copending application, Serial No. 738,327, filed May 28, 1958, now abandoned.

The preferential offset plan may include free operation of local controllers when traffic is light, two or three levels of inbound preferential offset, a nonpreferential one-block alternate offset when traffic is balanced, two or three levels of outbound preferential offset, and a nonpreferential multi-block simultaneous offset when traffic is saturated.

The nonpreferential offset plan may include free operation when traffic is light, a three-block alternate pattern as traffic increases, a two-block alternate pattern as traffic increases further, a one-block alternate pattern for heavy traffic, and simultaneous operation when traffic is saturated.

Traffic cycle offset is here defined as the percent of a traffic signal cycle that the start of a traffic cycle at a local intersection is delayed from the start of the cycle at a master controller. Progression, or movement of vehicles along a street at a constant velocity, is established by delaying the start of the right-of-way signal indication at successive intersections with respect to prior intersections. The amount of delay at each intersection is determined by the distance between intersections and the velocity of travel desired.

Preferential offset is defined as a form of progression that aids the flow of traffic in one direction but inadvertently slows traffic in the other direction.

In the nonpreferential, three-block alternate pattern the signals at each group of three contiguous intersections are timed in unison so that traffic may move uninterrupted in either direction through three intersections during one right-of-way interval, and then through three more intersections during the ensuing right of way interval, and so on. In a two-block alternate pattern two intersections are set at zero offset, two at 50%, two at zero offset, and so on, so that traffic may move two blocks during one green interval, two blocks during the ensuing green interval, and so on, without a stop. The standard system of traffic control now in general use where successive intersections are one-half cycle apart is called the one-block alternate pattern.

It is well known to program various progressive offset patterns according to known and anticipated traffic conditions. It is also known to vary a progressive offset pattern according to actual traffic conditions as determined by traffic sampling, What is believed to be new to the art is an improved apparatus for determining when the change in offset should take place, plus the ability of the apparatus to select one of a number of levels of progressive offset to favor one or the other direction of traffic. Another feature of the invention provides for selection of one of a number of multi-block alternate offsets determined by traffic volume. Multi-block alternate offset patterns have the advantage that they do not penalize traffic moving in the opposite direction. Still another feature of the invention provides that the various offsets be selected at various ratios of traffic density rather than on the basis of difference in density of traffic in two directions. This is believed to lead to more uniform selection of offsets at the various levels of traffic density.

The apparatus includes two traffic density computers one to compute traffic density in each direction, a balance detector to determine the higher density, various ratio detectors to determine the ratio of higher to lower density, an offset selector in the master controller, and cooperating apparatus in each local controller. One of a plurality of offsets favoring either direction of traffic may be selected. The choice of one of the various. offsets may become effective at the same or different levels of traffic density for the two directions. That is, a first progressive offset favoring inbound traffic may be selected at a ratio of inbound to outbound traffic of /45, for example, and a second progressive offset selected at a ratio of /40, while two progressive offsets favoring outbound trafiic may be selected at the same or different density ratios. For example, the different ratios used may be 57/43 and 63/37, or any other ratios. Any suitable ratio of densities may be used simply by presetting the ratio on one of the plurality of potential dividers provided.

It is noted above that different ratios may be used to establish a given offset for the different directions of traffic. In the prior art, offset selectors made no provision for such a choice. The reason that it is important to provide for such a choice is to give flexibility to the trafiic control system. In many locations the highway configuration favors traffic flow in one direction. This is only one example of such an unbalance of conditions that the invention aims to correct.

The invention is considered to be an improvement over known systems in that the apparatus is designed specifically for the function it is to perform and does not consist of a combination of apparatus designed for other uses. By way of illustration, the known apparatus improved upon :by the present invention consists of two known traffic cycle duration selectors and a third device to observe the position of two such cycle duration selectors and award a preferential offset accordingly. The invention consists of an offset selector operating directly from data received from two electronic traffic density computers. A greater range of stepless values of data may thus be compared within the invention, resulting in a greater degree of accuracy and permitting selection of one of a larger number of offsets.

The system is new in its ability to select one of a num- 'ber of offsets for each direction of traffic. Previously, only one offset was available for each direction of traffic.

The system is an improvement on known systems in its ability to select offsets at a different ratio of inbound/ outbound traffic volume then at outbound/inbound ratio. Known Systems use the same ratio for both directions.

The system is an improvement over known systems in that it can select m ulti-block alternate offsets at successive intersections which do not penalize traffic in the lesser direction. Prior systems awarded preferential offsets which cause traffic in the non-preferred direction to travel against the lights and stop at many intersections.

Objects The primary object of the invention is to provide a device which will select an offset favoring traffic in One direction at one ratio of inbound to outbound traffic density and which will select a similar offset favoring traffic in the other direction for the same or a different ratio of outbound to inbound traffic density.

Another object is to provide a device which will select one offset as the ratio of traffic density in one direction to traffic density in the opposite direction rises to a given value and a greater offset as the ratio rises to a second value.

Another object isto provide a device which will select said two offsets for different ratios of traffic flow in one direction than in the other direction.

Another object is to provide means for selecting a threeblock alternate traffic cycle offset when the level of traffic in the heavier direction exceeds a preset value, for selecting a two-block alternate cycle when the level exceeds a higher value, and for selecting a one-block alternate cycle when the level exceeds a greater value.

Another object is to provide means for measuring the ratio of traffic in two directions and making the offset selector inoperative when traffic is substantially balanced, permitting the local controllers to seek a balanced offset.

The invention will be described with reference to the following figures, of which:

FIGURE 1 is a plan view of a highway having detectors therein, inbound and outbound traffic density computers, an offset selector, and a cable interconnected to local controllers at each intersection.

FIGURE 2 is a block diagram of a simplified form of the offset selector apparatus.

FIGURE 3 is a block diagram of the preferred form of the offset selector apparatus.

FIGURE 4 is a wiring diagram of the offset selector apparatus.

FIGURE 5 is a diagram of the offset selector mechanism within a local controller.

FIGURE 6 is a wiring diagram of the offset selector and resynchronizing mechanism in a local controller.

General description A plan view of a typical installation is shown in FIG- URE 1. A highway is defined by the boundary lines HY. Intersecting the highway are a number of streets ST. Many or all of the intersections are signalized by traffic signals S, controlled by local traffic signal controllers LC.

In each highway lane 16 are mounted traffic actuable devices Dl-D6, each adapted to close a contact upon passage of a vehicle. Detectors D1-D3 monitor inbound traffic and supply signals to the inbound traffic density computer IC. Detectors D4-D6 monitor outbound trafhe and supply signals to the outbound traffic density computer DC. More or fewer detectors may be used, depending on the number of highway lanes in use. Any of the known types of detectors may be utilized; pressure, electromagnetic, electrostatic, photoelectric, infrared, radar, or any combination thereof. Pressure type detectors are shown for convenience only.

The function of the traffic density computers is to supply an output proportional to traffic density as reflected in impulses received from the detectors in the sampled lanes. One type of computer especially adapted to this use is disclosed in United States patent application 738,327, filed May 28, 1958, entitled Traffic Lane Control. Each such computer is equipped with individual input circuits for each traffic lane. This permits the unit to distinguish between closely spaced signals as from vehicles traveling abreast and actuating the detectors almost simultaneously. The signals are amplified, filtered, and reduced by a factor of two to permit the count to reflect the number of vehicles, not the number of axles. (A pressure sensitive detector puts out two signals for each vehicle passing over it, one for each axle.)

The amplified signals are given a uniform, adjustable duration and amplitude so that they may have equal weight in the count. A linear integrator averages the count over a short interval to provide an almost in stantaneou-s traffic density average and then feeds the count to a long-time integrator. The latter integrator averages the count over a longer, adjustable interval and develops an output potential substantially proportional to traffic density in one direction. The output may be something other than a potential; it may be a frequency, or a wave shape, or other output, or combination thereof, related to traffic volume density.

The output of each traffic density computer IC and OC is fed over lines 7 and 8, respectively, to the offset selector OS. The latter units weighs the two potentials against each other and determines which is the higher. If the higher potential is sufficiently great, each of the potentials is switched individually to a plurality of ratio detectors. If the ratio of the two potentials is sufficiently great, a first ratio detector will be energized to execute a first offset selection. If the ratio of the two potentials becomes great enough to cause a second ratio detector to be energized, a second offset will be selected. A time delay device may be included to maintain an offset for an adjustable time interval before a different offset may be put into effect. If traffic becomes balanced, the preferential offset may be eliminated and a standard, oneblock alternate traffic signal pattern may be instituted to favor each direction of traffic equally.

The electric signals needed to put into effect the various offset patterns are transmitted over conductors in an interconnecting cable CC or other channel to each local controller LC. The local controllers LC may be the type disclosed in United States Patent No. 3,133,264, entitled Multiple Program Traffic Control Systems. Controllers of this type are designed to receive signals from the offset selector OS and effect the necessary change in time of initiation of the traffic signal cycle.

The offset selector OS may be part of a more complex master traffic controller but is shown here separately for simplicity. Likewise, the traffic density computers may have additional uses and may supply their output potentials to other equipment within the master traffic controller effecting complete control of traffic within a highway system. The local controllers LC may also be of the type designed to effect all the necessary changes in the traffic signal cycle. These include traffic cycle offset, traffic cycle split, traffic cycle length, and resynchronization.

Various methods of transmitting the offset change signals to the local controllers may be used. These include one or more conductors, multi-conductor cable, leased telephone pairs, radio interconnection, microwave transmission, or by infrared.

A more complete description of the offset selector will now be given.

Offset selector Having given a broad description of the function of the offset selector, a description of a simplified version will now be made.

As shown in block diagram in FIGURE '2, the output potentials from the inbound and outbound traffic density computers IC and 0C are applied to a cathode follower amplifier CFA through conductors 7 and 8, respectively. The purpose of the cathode follower amplifier CPA is to develop a bias voltage for the electron tubes in the balance detector BD and to reduce the input potentials to a more useful range.

Potentials from the cathode follower amplifier CFA are applied to the balance detector BD where the higher potential may cause an electronic control device in the form of a tube to conduct thus energizing a plate circuit switching means in the form of a relay which switches said higher potential to a plurality of voltage dividers VDl, VDZ, and thence to one side of the ratio detectors RDl, RDZ. The lower incoming potential is switched directly to the other side of the ratio detectors RDl, RDZ.

Voltage dividers VDl, VD2 reduce the higher potential by two different adjustable percentages. Two different percentages are provided to permit the selection of different offsets at different levels of traffic density. For example, voltage divider VDll may be set at 75 percent resulting in the higher potential being reduced 25 percent. When the higher potential exceeds the lower potential by some percentage slightly greater than 33, it will cause ratio detector RDl to unbalance in favor of the higher potential and make effective a first offset change. This results when traffic in the heavier direction exceeds trafiic in the lighter direction by 100/75 percent or a ratio of 4 to 3.

To continue the example, voltage divider VDZ may be set at 60 percent resulting in the higher potential being reduced 40 percent. When the higher potential exceeds the lower potential by slightly more than 66 percent it will cause ratio detector RD2 to also unbalance and make effective a second offset change. This occurs when traffic in the heavier direction exceeds traffic in the lighter direction by 100/60 percent or a ratio of 5 to 3.

Each ratio detector RDl, RDZ consists of a double electronic control device in the form of a double triode vacuum tube with the cathodes connected in common through a cathode resistor as shown also in FIGURE 4. The lower output from the traffic density computers is applied to the input circuit or grid of one half of the tube through a dropping resistor. In its output or plate circuit is a resistor whose impedance is similar to that of the relay in the plate circuit of the other half of the tube. To the grid of the other half of the tube is applied the reduced higher voltage. When the ratio of the two voltages becomes slightly greater than the ratio preset on the bias resistors, the higher voltage permits its half of the tube to conduct sufficiently to pull in the ratio detector relay.

The ratio detector relay is necessarily small; therefore it is used to energize a relay in the slave relay circuit SR which in turn controls power to the offset selector conductors in the interconnecting cable CC.

Thus, the balance detector is able to distinguish the higher of the two potentials representative of traffic density and switch the higher potential through one or more voltage dividers and ratio detectors to determine the ratio of heavier to lighter traffic. When heavier traffic exceeds lighter trafiic by one preset ratio it effects one level of progressive offset in a favor of the heavier direction of trafiic. When heavier trafiic exceeds lighter trafiic by a second preset ratio it effects a higher level or progressive offset in favor of the heavier direction of trafiic. Thus, a total of four progressive offsets are available, two for each direction. A fifth offset favoring each direction equally is in effect when traffic density in each direction is substantially balanced.

A sixth plan may be put into effect when traffic density is very high in both directions. This plan may include the simultaneous operation of a large group of traffic signals along a thoroughfare. One example may be a four-block alternate plan with groups of signals at four succeeding intersections being operated simultaneously. By lengthening the traffic cycle and by including more signals in the alternate groups, heavy trafiic flows may be handled efficiently because time-consuming stops and starts are reduced. Apparatus at the local controller for effecting the various offsets is described in the final section of the present application.

The plan for simultaneous operation of groups of signals may be put into effect under one option when both halves of the balance detector BD are energized. This condition occurs when both potentials from the traffic denisty computers IC, 0C are high. When. both halves of the balance detector are energized they in turn cause the simultaneous operation apparatus S0 to be energized. The apparatus for simultaneous operation consists of two sets of relay contacts on the balance detector relays, a relay in the slave relay circuit SR, and a conductor therebetween. The apparatus operates through the slave relay circuit SR to effect the simultaneous operation plan at the local controllers by energizing one or more interconnecting conductors CC. The slave relay circuit SR consists of a group of relays, one energized by each ratio detector to cause the conductors in cable CC to be energized in various binary combinations.

The selector unit shown in FIGURE 2 is. designed to use the same ratios for each direction of traffic. It does not permit different ratios to be set for inbound/outbound ratios than for outbound/inbound ratios. To permit different ratios to be used, the device requires a second set of voltage dividers and ratio detectors as shown in FIG- URE 3 and described in the next section.

Preferred embodiment The essential difference between the apparatus shown in FIGURE 3 and that shown in FIGURE 2 is the addition of a second set of voltage dividers and ratio detectors.

To explain the function of the offset selector a typical traffic pattern will be described. Starting in the early morning hours frame is normally irregular and light. Density is insufficient to unbalance the balance detector BB in either direction and the normal pattern of one-block alternate signals is in effect. A one-block alternate pattern includes the display of right-of-way signals at alternate intersections and stop signals at the intersections inbetween.

As inbound traffic builds up during the morning, the output of computer IC also builds up and becomes sufficient to actuate balance detector BD and. is switched through the voltage dividers VDl-VD4 and then to ratio detectors RDl-RD4. It may soon become sufficient to unbalance the inbound lesser ratio detector RD] and energize line 61 to the slave relay circuit SR which in turn may energize a control conductor in interconnecting cable CC. The first inbound preferential offset will be placed in effect at the local controllers LC. If inbound traffic should build up sufficiently to actuate the inbound greater ratio detector RDZ, it would energize line 62 to the slave relay SR. A second control conductor in cable CC may then be energized. This will put into effect the second inbound preferential offset at the local controllers LC.

If now traffic should increase on the outbound lanes and/or decrease on the inbound lanes until the ratio of inbound to outbound traffic has decreased, the greater ratio detector may become de-energized. The inbound preferential offffset will then be reduced to the lower level. If traffic becomes sufliciently balanced, ratio detector RDl may be de-energized causing the local controllers to revert to the balanced, one-block alternate signal plan.

If traffic is both heavy and balanced, both sides of the balance detector BD may be energized causing simultaneous operation of the signals S through the SO device. The simultaneous operation device SO consists of two sets of relay contacts on the balance detector relays which energize line 65 and a relay in the SR unit to effect simultaneous operation of the local controllers LC.

The unit functions similarly when outbound traffic exceeds inbound traffic. The potential from the outbound computer 0C reduced through the outbound lesser voltage divider VD3 may be sufficient to outbalance the potential from the inbound computer IC when they are compared within ratio detector RD3. Ratio detector RD3 may energize line 63 to the slave relay circuit SR which in turn may energize a conductor in cable CC causing the outbound lower potential offset to be placed in effect at the local controllers LC. A higher ratio of outbound to inbound traffic may permit ratio detector RD4 to become unbalanced by the potential received through outbound greater voltage divider VD4. Ratio detector RD4 may energize line 64 and through slave relay circuit SR may energize one or more conductors in cable CC to make the outbound greater preferential offset effective at the local controllers LC.

An interlock circuit is provided as part of the balance detector BD which makes the outbound offset control circuits 63, 64 ineffective when inbound traffic is heavier. Likewise, when outbound traffic exceeds inbound traffic, the inbound offset control circuits 61, 62. are rendered ineffective.

The slave relay circuit SR may energize one or more conductors in the interconnecting circuit CC in various binary combinations to thereby control the offset mechanism in the local controllers. Use of a binary system requires fewer conductors in interconnecting cable CC.

It is to be noted that the adjustment of the offset control mechanism in each local controller LC actually determines what offset Will be in effect at that intersection when a particular control conductor or combination of control conductors is energized.

Thus, the levels of traffic cycle offset are matched to actual traffic conditions.

Wiring diagram A schematic wiring diagram of an offset selector permitting independent adjustment of the ratios for each direction of traffic is shown in FIGURE 4. Six electronic control devices, such as tubes, are employed in this embodiment with four of the devices used as ratio detectors. In another embodiment more or fewer ratio detectors may be employed without departing from the spirit of the invention.

One ratio detector stage is employed for each inde pendently adjustable ratio desired. For instance, tube V1 detects the lesser ratio of inbound to outbound traffic. When traffic exceeds the preset ratio, tube Vll energizes switching means in the form of relay CR1. Contacts on relay CR1 energize conductor 61 which energizes a load relay in slave relay circuit SR which in turn effects a first preferential offset favoring inbound traffic.

A second ratio detector tube V2 is employed to detect the greater ratio of inbound to outbound traffic. When traffic exceeds the preset ratio, tube V2 energizes switching means in the form of relay CR2 which energizes conductor 62 to pull in a load relay in slave relay circuit SR which in turn effects a second preferential offset favoring inbound traffic.

A third ratio detector tube V3 is utilized to detect the lesser ratio of outbound to inbound traffic. When trafiic exceeds the preset ratio, tube V3 energizes switching means in the form of relay CR3 which energizes conductor 63 to pull in a load relay in slave relay circuit SR which effects a first preferential offset favoring outbound traffic.

A fourth ratio detector tube V4 is utilized to detect the greater ratio of outbound to inbound traffic. When traffic exceeds the preset ratio, tube V4 conducts and energizes switching means in the form of relay CR4- which energizes eonductor 64 and causes a load relay in slave relay circuit SR to effect a second preferential offset favoring outbound traffic.

When traffic is very heavy both halves of the balance detector electron control device in the form of tube V6 are conducting sufficiently to energize plate circuit switching means in the form of relays CR5 and CR6, closing contacts CR5-7 and CR6-7 energizing conductor 65. The controllers along the thoroughfare may go to simul- 8 taneous operation, allowing clear passage during the major portion of each traffic signal cycle.

When traffic is light and neither half of the balance detector V6 is energized, a balanced pattern of operation is put into effect with the signals reverting to the standard, one-block alternate pattern. The offset favors neither direction.

Thus the unit serves two functions; it discerns which direction of traffic is heavier, and it compares the ratio of heavy to light traffic against two independently adjustable ratios to determine which direction of traffic shall be favored with the offset, and what the level of offset shall be.

Referring to FIGURE 4 in greater detail, the output of the inbound traffic density computer IC is fed in on pin P4, through potentiometer R1 and resistor R2 to the grid V5G1 of the tube half VSA of the electronic control device taking the form of tube V5. The output of the outbound traffic density computer 0C is fed in on pin P7, through potentiometer R3 and resistor R4 to the grid V5G2 of tube half VSB.

Tube V5 serves as a cathode follower amplifier CFA. The tube half which has the higher potential impressed on its grid conducts more heavily. The cathode to plate current flowing through the tube VSA increases the voltage rise across resistor R5 and increases the bias voltage on grid V661 of tube V6A. The current flowing through tube VSB increases the voltage rise across resistor R6 and increases the bias voltage on grid V662 of tube VGB. In the present embodiment the peak potential of approximately 50 volts delivered by the computers IC, 0C is reduced to approximately 15 volts to permit the balance detector V6 to discriminate more accurately between potential changes.

The tube half V6A or V6B which has the least negative potential impressed on its grid conducts more heavily and may energize plate circuit relay CR5 or CR6. When one direction of traffic is sufficiently heavier than the other, the relays switch the computer potentials to the ratio detectors, the higher potential being switched through the potentiometers PD1-PD4 and the lower potential through the lower valued fixed resistors R11- R14. Relays CR5 and CR6 also determine which of the ratio detectors is to be effective, inbound or outbound, and switch power through line 51 or line 54 to the ratio detector relay contacts accordingly.

The otentiometers associated with the ratio detectors may be adjusted to provide the various ratios desired for offset change. To illustrate the settings in relation to the conditions enumerated in the first paragraphs of this section, potential divider PDl associated with tube V1 may be set for any ratio between 1 to l and 1.5 to 1. When the ratio of inbound to outbound traffic exceeds the preselected value set between 1 to 1 and 1.5 to l, relay CR1 is energized making the first inbound preferential offset effective.

Potential divider PD2 associated with tube V2 may be set for any ratio between 1.5 to l and 2.5 to 1. When the ratio of inbound to outbound traffic exceeds the preselected value set on potential divider PDZ, relay CR2 is energized making effective the second inbound preferential offset. This allows inbound traffic relatively free movement.

Potential divider PD3 associated with tube V3 may be set for any ratio between 1 to l and 1.5 to 1. When the ratio of outbound to inbound traffic exceeds the preselected value relay CR3 is energized making the first outbound preferential offset effective.

Potential divider PD4 associated with tube V4 may be set for any ratio between the preselected value and 2.5 to 1. When the ratio of outbound to inbound traffic exceeds the preselected value, relay CR4 is energized making effective the second outbound preferential offset.

The function of the offset selector will now be explained in relation to a normal pattern of traffic buildup. Assume that early morning traffic is light and is predominantly inbound. If inbound tramc is sufficiently heavier than outbound, it will permit relay CR to pull in closing contacts CR51 and 2 and contacts CR5-4 and 5. Now-closed contacts CR5-1 and 2 apply the potential arriving from the outbound computer OC through pin P7 through conductor 53 to the grids V161, V2G1, V361, and V4G1 of the ratio detector tubes. The potential is dropped through fixed grid resistors R11, R12, R13, and R14 associated with tubes V1A, VZA, V3A, and VIA, respectively. The lower input potential is thus applied to the fixed resistors.

The output of the inbound computer IC arriving through pin P4 is now fed through contacts CR6-3 and 2, through conductor 52 to the potential dividers PD1, PD2, PD3, and PDdassociated with tubes V1B, VZB, V3B, and V4B, respectively. The tap on each potential divider applies a reduced voltage to the grids V1G2, V2G2, V3G2, and V4G2, respectively. The taps may bet set for the various ratios desired for levels of offset change as illustrated above. If the ratio of inbound to outbound trafiic is high enough to cause the right half of ratio detector tube V1 to conduct, plate circuit relay CR1 will be energized.

Energization of relay CR1 closes contacts CR1-1 and 2 permitting power to flow from terminal L2, through line 50, through contacts CR6-6 and 5, through contacts CRS-S and 4, through line 51, through now-closed contacts CR1-2 and 1, to output conductor 61. In the slave relay circuit SR shown in FIGURE 3 conductor 61 energizes a relay which in turn energizes a control conductor in the interconnecting cable CC. Thelslave relay circuit SR consists of a group of relays one for each ratio detector and is provided to increase the current carrying capacity of plate circuit relays CRl-CR i, which are necessarily small. The slave relay circuit SR also converts the output to a binary output in a binary switching arrangement which permits up to eight items of information to be transmitted over a three conductor cable and common return conductor. Various conductors are energized in unique patterns to provide a plurality of unique outputs.

Assume now that inbound traffic becomes heavier and that it exceeds outbound traffic by the preselected ratio, say, for example, 1.6 to 1. The right half of balance detector tube V1 continues to conduct maintaining relay CR1 energized. The left half of tube V2 begins to conduct sufficiently to energize relay CR2. Tube halves V1B and V2B will thus be conducting sufiiciently to energize relays CR1 and CR2, respectively, because the ratios of higher to lower potential are within the ratios set on potential dividers PD1, PDZ. With the energization of relay CR2, contacts CR2-1 and 2 close permitting L2 power to flow to output conductor 62 associated with the greater in'bound preferential offset. Closure of contacts CR31 and 2 and contacts CR41 and 2 has no effect because contacts CR64 and 5 are open preventing L2 power from reaching output conductors 63 or 64.

Assume again that traffic is light but increasing on the outbound lanes. If outbound traffic becomes sufiiciently heavy it will unbalance the balance detector tube V6 and energize relay CR6. Contacts CR61 and 2 will close applying the higher potential arriving on pin P7 to potential dividers PD1-PD4 over conductor 52. Contacts CR5-2 and 3 are closed applying the lower potential arriving on pin P4 to the fixed resistors Ell-RM over conductor 53. if the ratio of outbound to inbound traflic exceeds the preset ratio set on potentiometer PD3, tube half V3B will conduct energizing relay CR5.

Relay CR3 will close contacts CR31 and 2 permitting power to flow from terminal L2, through line Sfi, through contacts CR56 and 5, through contacts CR6-5 and 4 through line 54, through contacts CR32 and 1 to conductor 63. Conductor 63 energizes a relay in the slave if) relay circuit SR which may energize a control conductor in the interconnecting cable CC which effects a change at the local controllers LC to a first preferential offset for outbound traffic.

If outbound traffic continues to build up until it exceeds inbound traffic by the preselected ratio, say 1.9, for example, relay CR4 will be energized. Conduction through tube half V413 will result from the increased potential developed by the outbound computer feeding in on pin P7, flowing through contacts CR6-1 and 2, conductor 52, potential divider P134, and grid V4G2. The increase in potential causes tube half V4B to conduct, energizing relay CR4, closing contacts CR4-1 and 2, energizing output conductor 64. Conductor 64 is associated with a relay in slave relay circuit SR which effects the change in offset to the greater outbound preferential offset.

Conductor 63 is still energized because relay CR3 is energized. Conductors 61 and 62 are de-energized because contacts CR54 and 5 are open.

If traffic is very heavy in both directions, both balance detector relays CR5 and CR6 will be energized, Contacts CR57 and CR67 will be closed admitting L2 power to flow over conductor 65 to the slave relay circuit SR where it energizes a relay which de-energizes all interconnecting conductors CC. As shown in Table 1 (shown below) when all interconnecting conductors CC (22, 23, 34) are de-energized the local controllers assume simultaneous operation.

A description of the apparatus which effects the offset changes at the local controllers LC is shown below after the following section.

Alternate offsets A pattern of non-preferential offsets may be better suited to some city street configurations than levels of preferential offset. Preferential offsets give advantage to trafiic moving in one direction, to the disadvantage of traffic moving in the opposite direction. A system of nonpreferential offsets has been devised which permits more rapid movement of traflic in both directions when traffic is light. As traffic volume increases and begins naturally to move slower, the offset is revised to permit such movement. As traffic becomes dense and moves slowly and cautiously, offset is further tailored to meet the speed established by the flow of traffic.

The volume of traffic moving in the heavier direction determines which offset should be in effect. The lesser volume is permitted to move in the opposite direction under the same signal conditions, which will permit lighter trafiic to move more rapidly simply because there are fewer vehicles using equal highway facilities. However, this is a windfall advantage to traffic in the lighter direction. Equal advantage could be given to trafiic in each direction by reducing the number of lanes open to trafiic in the lighter direction and transferring these lanes to use by traffic in the heavier direction. Apparatus designed to accomplish such lane transfer is disclosed in United States patent application 738,327, entitled Traflic Lane Control, noted above.

The pattern of non-preferential offsets described above may include the standard one-block alternate pattern when traffic is most dense, a two-block alternate pattern when traffic is medium, and a threeor four-block alter nate pattern when traffic is light.

A one-block alternate pattern is described as a pattern of signals along a thoroughfare illuminating the green signal at one intersection, red at the second, green at the third, red at the fourth, and so on. A two-block alternate pattern illuminates the green signal at the first and second intersections, the red at the third and fourth intersections, the green at the next two, and s0 on. If the cycle lengths were identical it can be seen that traffic in both directions may move twice as fast with the two-block alternate system.

A three-block alternate pattern illuminates the green signal at the first three intersections, the red signal at the next three intersections, and the green signal at the next three. Under conditions of light traffic, vehicles may move at three times the speed they are permitted under heavy traffic conditions. To avoid excessive traffic speed, the cycle length may be increased so that traffic will have an increased time to travel through three intersections during one-half cycle. During periods of light traffic the traffic cycle split between main street and cross street may be changed to favor main street thus increasing the duration of the right-of-way interval to main street and permitting slower movement of traffic.

The offset selector apparatus disclosed herein is adaptable to select any of the offsets here described and any other type of offset that the traffic engineer may specify. The ratios of heavier to lighter traffic density at which the various offsets are selected are settable on adjustable potentiometers PDl-PD4. The desired offsets are presettable at each local controller simply by turning a dial, one for each offset. Each dial reads directly in percent of the traffic cycle that the particular local controller is to lead or lag the cycle at the master controller. Settings are made more exact by referring to a time-space diagram for the thoroughfare. Such diagrams are simple to devise and are known to all trafiic engineers.

The preferred form of the offset selector mechanism within the local controller is described below.

Local ofisct mechanism One form of apparatus designed to effect the change in offset at each local intersection traffic controller is shown in plan view in FIGURE 2 and in sectional View in FIG- URE 5 in United States patent application 642,469 noted above. The wiring diagram for such apparatus is shown in FIGURE 7 of that application.

A new, preferred form of the apparatus is shown in FIGURE 5 of the present application. The relevant portion of the above mentioned wiring diagram is reproduced in FIGURE 6 of the present application. The same numerical designations are used in both applications to avoid confusion. The new wiring diagram has been expanded to include the six offsets shown in FIGURE 5.

In the above-identified application, the offset cam pairs 116-119 are arranged on a common shaft 8 and secured with set screws making their adjustment somewhat difiicult. In the present application, each offset cam pair 116, 117, 118, 119, 220, 221 is mounted on an individual shaft driven by a common gear 215 on shaft 298 and is readily adjustable from the front of the panel. Two additional cam pairs 220, 221 have been added to provide the preferred number of offsets.

The function of the offset selector is to rotationally displace the cycle timing dial 202 with respect to its zero reference or resynchronizing cam 264. This is accomplished by temporarily energizing the reversible offset drive motor 114 through one of the six selector switches 116S-119S, 220$, 2218, in circuit with one of the six reversing switches MGR-119R, 220R, 221R. While reversible mot-or 114- is energized it also drives cam sets 116- 119, 220, 221 to de-energize itself when it has applied the offset desired. Which switch and cam pair 116119, 220, 221 is effective to determine the offset is determined by the relative position of relay contacts 125, 138, and 145, FIGURE 6. The position of contacts 125, 135, and 145, FIGURE 6, is determined by the electrical condition of interconnecting conductors 22, 23, and 34, respectively. The slave relay circuit SR shown in FIGURE 3 determines which interconnecting conductors are to he energized. Motor 114 displaces the cycle timing dial 202 with respect to its zero reference cam 2 4 with local power which is disconnected by switches 1165-1193;, 220$, 2215 when the desired offset is completed An offset change will be illustrated more completely with reference to FIGURE 5. Assume that traffic conditions have been stabilized for a time sufficient for a first inbound preferential offset to have been effected. At the particular local controller LC being observed, one cam of cam pair 119 has actuated switch 119$ causing it to open and disconnect motor 114 from its source of power L2. The other groups of switches are ineffective because relay contacts 125, 138, 145 are in the position shown in FIG- URE 6. interconnecting conductor 34 was energized when the first inbound preferential offset was selected and remains energized. Relay coil 14 was energized by conductor 34, closing contacts 145 into the position shown in FIGURE 6. While the first offset was being accomplished current flowed from line L2, through relay contact 148, through relay contacts 135, through relay contacts 128, through switch 1198, through switch 119R, through line 129, to motor 114.

While motor 114, FIGURE 5, was energized it transmitted torque through its pinion 204, gear 205, shaft 98, gear 115, gear 91, and the hub of gear 91 to the fixed gear 93 of the differential. Normally, the fixed gear 93 permits the torque applied by the constantly running, variable speed motor to be applied through shaft 262, to ring gear 92, to pinion 95, to shaft 96 attached thereto, to pinion 206, to internal gear 207 of timing dial 202. Now, with torque applied to normally-fixed ring gear 93, dial 202 is rotationally displaced with respect to cam 264 which is the zer0-reference cam kept in constant time with the zero point in the traffic cycle as established by the master controller. Cam 264 is geared to rotate at the same speed as dial 202.

Thus, the timing dial 202 is offset with respect to the master cycle. For this reason the apparatus is termed an offset selector.

Assume now that traffic conditions change such that a second level of preferential offset is demanded by inbound traffic. Inbound ratio detector tube V2 at the master controller energizes relay CR2, FIGURE 4. Relay contacts CR2-1 and 2 being closed permit power to flow from terminal L2 to output conductor 62. Conductor 62 energizes a relay in slave relay circuit SR which in turn energizes one or more interconnecting conductors CC. In this example conductor 22 is energized. Conductor 22 energizes relay coil 13 in each local controller which closes contacts 138. Power will flow from line L2, through relay contacts 148, through the lower of contacts 138, through contacts 128, through switch 1175 which is closed until the offset is completed, through contacts 117R, and over lines 128 or 129 depending on the relative position of reversing switch 117R, to motor 114. Motor 114 is energized in either the forward or reverse direction, whichever requires the least rotation for the cam of cam pair 117 to reach and actuate switch 1175. The direction of travel is determined by the front halfsegment cam of cam pair 117. When switch 1178 is momentarily opened on the rise of cam 117, the circuit to motor 114 is broken and motor 114 and gear train stop, looking gear ring 93 and making variable speed motor 60 the sole source of torque for timing dial 202.

Cam pairs 116, 117, 118, 119, 220, 221 have been previously manually adjusted for the offset desired at each local controller according to time-space diagrams for the thoroughfare.

The apparatus operates in like manner when any other offset is selected by the master offset selector OS and slave relay circuit SR. Energizing or de-energizing one or more of the conductors 22, 23, 34 in the interconnecting cable CC serves to operate relay contacts 138, 128, 148, respectively. The relative position of the relay contacts determines which switch 116$, 117$, 118$, 119$, 220$, 2215 provides a path for the energization of reversible motor 114. Because the cams may be disposed in different arcuate relationships with respect to a zero offset position they travel ditferent distances in reaching their home position. While they are traveling, the torque used to home them is also applied to timing dial 202 causing it to be rotated an equal number of degrees with respect to the zero reference or resynchronizing cam 264. Thus, any of the offsets set on the dials may be obtained from the master offset selector OS.

Table I below notes the condition of the various interconnecting conductors and relays for the different offsets available. More or fewer offsets may be employed without departing from the spirit of the invention.

TABLE I.-LOCAL CONTROLLER OFFSET CONTROL UNDER VARIOUS TRAFFIC CONDITIONS interconnecting Local Controller Local Controller Conductors Energized Relays Energized Switches Energized Offset Desired 34 22... 23 14 l3 l2 Free. Dwell in Main Street 221R.

Green Interval.

1st Inbound Offset On On 119R. 2d Inbound Oflsetnnr On On. On 117R 3d Inbound (Optional). On Not Shown Average Offset On On On On 116R. 1st Outbound Ofiset On 220R. 2d Outbound Offset On On On 118R. 3d Outbound (Optional) On On On On Not Shown Simultaneous Signal Change 22lS 221R 2 1 Resynchronizing Street green interval.

I 1 Besynchronization is permitted to function to tion. The cycle length may be increased to permit The switches and cams employed for the third inbound and outbound offsets are omitted from the wiring diagram and the apparatus drawing to simplify these drawings. One skilled in the art could add the additional cam pairs similar to those shown at 116419, FIGURE 2, application 642,469, or those shown at 116-119, 220, 221, FIG- URE 5 of this application.

Non-preferential ofisets The various trafiic plans employing non-preferential offsets will now be explained in greater detail. The more common non-preferential offset plans include free operation, average offset, and simultaneous operation.

Free operation is here defined as a traffic plan permitting all controllers along a thoroughfare to dwell with rightof-way signals illuminated on the thoroughfare and permitting semiand full-actuated controllers to answer calls on the cross street during a selected portion of the traffic signal cycle as established by the master controller.

Average offset is here defined as one of a group of traffic plans, each of which permit equal traflic progression in each direction. Examples of average offset are the one-block alternate plan, two-block alternate plan, etc.

Simultaneous operation may be defined as a traffic plan permitting all traffic signals along a thoroughfare to be operated in unison. All the right-of-way signals along the thoroughfare are illuminated during one portion of the cycle, and all the cross street signals are illuminated during the second portion of the cycle. The cycle may be lengthened to permit a larger number of vehicles to move during the right-of-way interval.

The preferred method of selection of the non-preferential offset plans will now be explained.

Free operation of all controllers along a thoroughfare may be permitted when traffic is very light, as for example from 12 pm. until 5 am. Semi-actuated or fullactuated controllers are permitted to dwell giving main street the right-of-way and are permitted to answer traffic detector actuations on the cross street whenever they occur. Non-actuated controllers may be permitted to dwell with a flashing amber signal to main street and a flashing red signal to cross street. Nonactuated controllers may also be permitted to dwell with the green signal illuminated to main street traflic and the red signal to cross street traflic although it is considered by some traffic engineers to be poor practice to permit the green signals to be illuminated all along main street the entire time because drivers tend to increase their speedto make as many green lights as possible.

Free operation is effected when both balance detector potential is on continuously to cause all local controllers to stop and dwell in the Main perfit all local controllers to assume the zero offset posi traffiie to travel further during the green interval.

must be set at zero. All the controllers are thus allowed to fall into synchronism. This may require one or more traffic signal cycles. When sufficient time has elapsed so that it is certain that all of the local controllers are operating at zero offset and in step with the master con troller, the controllers may be stopped with their main' street right-of-way signals illuminated. To stop the controllers in the main street green interval the resynchro nizing circuit which is normally tie-energized by the master controller once each cycle is now not de-energized. Referring to FIGURE 6, the local. resynchronizing circuit includes interconnecting conductor 21, con tact 67 operated by zero reference or resynchronizing cam 264, and relay coil 27. Normally, resynchronizing potential is sent from the master controller over conduc tor 21 for 97% of each traffic signal cycle. Contact 67, being open 98% of each local trafiic signal cycle, prevents relay 27 from being energized when the local c011- troller is in step with the master controller. When the resynchronizing potential is applied continuously and zero reference cam 264 rotates sufficiently to close contact 67, relay 27 is energized, contact 278 is opened and timing motor is deenergized. (Relay 26 is continuously energized from the variable frequency potential applied at the master controller to interconnecting conductor 20. If the variable frequency potential fails, contacts 263 apply local L2 power to motor 60.)

Thus, by not interrupting the resynchronizing potential, each local controller is caused to stop and dwell in the main street right-of-way interval.

The resynchronizing potential is not made continuous until all of the local controllers have had time to ar rive at the zero offset position. This may be 5 minutes in the embodiment of the apparatus described. A time delay relay (not shown) may be employed at the master controller to obtain this delay.

Average offset, another type of non-preferential offset, may be selected when traffic is heavy and balanced. When inbound and outbound traflic is relatively balanced and of substantial volume both balance detector relays CR5 and CR6, FIGURE 4, are energized. Power is removed from the ratio detector relay contacts CRi-Z, CR2-2, CR3-2 and CR4-2 and thereby from control conductors 61-64. Auxiliary contacts CR57 and CR6- 7 close permitting power to flow from terminal L2 through relay contacts CR5-7 and CR67, and through conductor to slave relay circuit SR. In the latter circuit, not shown, the power is utilized to energize one or more relays which in turn energize interconnecting conductors 22, 23, and 34. Conductors 22, 2:3, and 34 15 serve to energize relays 13, 12 and 14 respectively and make switches 1168 and 116R effective to change the offset. Offset dial 116 in the local controllers LC may be set to provide a one-block alternate pattern.

Simultaneous operation, another type of non-preferential offset, may be selected optionally under one or the other of the following conditions: when trafiic in one direction is saturated, or when traffic in both directions is saturated. If simultaneous operation is to be selected when trafiic in either direction is saturated, it may be put into effect in place of the third preferential offset for either or both directions. If simultaneous operation is to be selected only when traffic in both directions is saturated, it may be put into effect when both balance detector relay CR5 and CR6 are energized.

The simultaneous offset is selected at the local controllers LC when interconnecting conductors 22, 23, and 34 are all de-energized. These conductors are de-energized by slave relay circuit SR. The slave relay circuit SR must be jumpered or rewired to fit the option desired. Thus, if simultaneous offsets are to be selected when the highest ratio detector in either direction is energized, slave relay circuit SR must be wired to permit the relays therein to deenergize interconnecting conductors 22, 23 and 34 when either control conductor 62 or 64 is energized. If three preferential offsets (not shown) are provided for each traffic direction, then control conductors 66 or 67 (not shown) controlled therefrom, must be effective to de-energize interconnection conductors 22, 23, and 34.

If the simultaneous offset is to be selected when trafiic in both directions is heavy and balance detector relays CR5 and CR6 are energized, an additiional set of contacts CR57 and CR6-7 are employed to energize through conductor 65 one or more of the relays in slave relay circuit SR which in turn de-energize interconnecting conductors 22, 23 and 34.

It is to be noted that two conditions, free operation and simultaneous operation, are both obtained by the same de-energized condition of interconnecting conductors 22, 23 and 34. There is a difference, however. The free operating condition is obtained by continuously energizing the resynchronizing line 20. Each of the local controllers is made to stop and dwell in the main street green interval. The simultaneous operating condition is obtained by normal operation of the resynchronizing line 20. All of the local controllers assume the zero offset position and then operate in unison and in synchronism.

The circuitry within the slave relay unit SR is not shown because the circuit is not novel, as anyone skilled in the art may diagram and make the necessary connections. The circuit serves to convert electric data received over four or more conductors 6165 to data that may be sent over three conductors 22, 23, and 34, by energizing the latter conductors in unique binary combinations.

Within each local controller LC the selection of the simultaneous offset is effected simply. Identical offset dials in each controller are set for zero offset. Referring to FIGURE 5, the dial fixed to cam pair 221 may be chosen and set at zero in every local controller. Then, when interconnecting conductors 22, 23, and 34 are deenergized and switches 2218 and 221R become effective, reversible motor 114 will be energized to rotationally displace timing dial 202 slowly to zero offset with relation to zero reference or resynchronization cam 264. When each timing dial 202 arrives at the point of zero offset, motor 114- is de-energized and only timing motor 60 continues to drive timing dial 202.

S ummary It has been shown that the preferred embodiment of. the invention adjusts itself rapidly to varying traffic conditions and is also readily adaptable to different high applications.

The traffic cycle offset selector is able to select from among a preset group of offset plans the one most favorable to actual traffic conditions. The instantaneous condition of traffic in each of two opposing directions is determined by two traffic volume or density computers. A balance detector and a plurality of ratio detectors allow the heavier traffic volume to determine the traffic plan selected.

A typical daily pattern of operation may begin with the local intersection controllers operating free. Traffic ac tuated controllers dwell with the green signals illuminated to main street traffic, and answer detector calls from cross street traffic as they occur. Non-actuated controllers dwell with the main street amber signals flashing giving the right-ofway to the main street, and the cross street red signals flashing requiring cross street traffic to stop and then proceed when no trafiic impedes their passage.

As traffic volume increases a different plan may he put into effect. If traffic builds up in one direction faster and/ or heavier than the other direction a first preferential offset may be put into effect. Various levels of preferential offset are called into play as various levels of traffic occur. If the two directions should become equal, an average offset may be effected.

- if now traffic increases in the opposite direction or decreases in the first direction, a preferential offset may be put into effect to favor the opposite direction of traffic. Various levels of preferential offset are available to meet varying traffic demands. The offset may move from one level to a higher or lower level without going through a level not demanded.

If traffic should become saturated in one or both directions, a simultaneous plan may be put into effect. This plan permits all of the right-of way signals along a thoroughfare to be illuminated in unison to move large volumes of traffic. During the latter portion of each cycle the signals stop through trafiic and permit cross street traffic to move. After the rush when traffic volume decreases, a level of preferential offset may be selected. As traffic decreases, the offset may move down the scale of levels of preferential offset to an average offset or to free operation.

A second series of offset plans is available by presetting a different group of offset percentages on the offset dials within each local controller. These plans may include a three-block alternate signal pattern when traffic is light and moves freely along the thoroughfare, a two-block alternate pattern when traffic is heavier, and a one-block alternate pattern when trafiic is heavy. The free pattern is available if desired when tr aflic is very light, and the simultaneous pattern is available when the thoroughfare is saturated.

The plans and patterns selected may be determined by the traffic engineer at the time of installation. The configuration of the highway and other conditions will determine the patterns chosen.

I claim:

1. In a traffic control system for use along a thoroughfare having inbound and outbound lanes and traffic actuable detector means for detecting traffic in each said lane, comprising traflic density computing means for developing output signals representative of the magnitude of traffic density in each said lane, balance detector means for determining the output signals of greater and lesser magnitude and developing a pair of first switching signals in accordance therewith, a plurality of ratio detector means each for determining the ratio of the magnitudes of said output signals and developing a second switching signal when said ratio is greater than a predetermined ratio, first switching means connecting said computing means to said ratio detector means and responsive to said first switching signals above a predetermined value to actuate at least one of said ratio detector means, a plurality of preferential offset control circuits, and second switching means connected to each said ratio detector means and to one of said preferential offset control circuits and responsive to said second switching signal to connect said one preferential offset control circuit with a voltage source for energizing same.

2. In a system for control of traffic in two directions along a thoroughfare, including, in combination: traffic actuable detector means for detecting traffic in the traveled lanes of said thoroughfare, inbound and outbound traffic density computer means responsive to actuations of said detector means and developing outputs representative of the traffic density in each of said lanes, a plurality of ratio detectors for each direction of traffic, balancedetector means for receiving and comparing the outputs of said computer means, first switching means controlled by said balance detector means to apply the outputs of said computer means to said ratio detectors, second switching means connecting a plurality of interconnecting channels to said ratio detectors, a plurality of intersection traffic signal controllers each having a plurality of independently adjustable offset securing means, each said offset securing means having energizing means connected to said interconnecting channels through relay means to permit only one offset securing means to be energized and effective at a time until it has secured its preset offset.

3. A vehicular traffic control system for a plurality of intersecting streets comprising, traffic actuated means for detecting traffic individually in both directions on at least one of said streets; at least two traffic volume computer means, each responsive to actuations of one of said detector means and developing a potential proportional thereto; a plurality of ratio detector means; a like plurality of potential divider means, each connected to one side of one of said ratio detector means; balance detector means responsive to said computer means to determine the higher of said potentials; switching means controlled by said balance detector means for applying the higher potential across said potential divider means and the lower of said potentials directly to another side of each said ratio detector means; a plurality of local traffic signal controllers; offset selector means in each of said controllers; interconnect-ing channels connecting said ratio detector means and said offset selector means, traffic cycle timing means in each of said controllers; and said offset select-or means controlling said cycle timing means in accordance with said traffic volumes in opposing directions.

4. An offset selector for use with a traffic control system having inbound and outbound lanes and trafiic actuable detector means for detecting traffic in each said lane and providing output detector signals in accordance therewith, said selector comprising a pair of traffic density computer means responsive to said output detector signals of said traffic detector means for developing output signals proportional in magnitude to traffic density in opposite directions, balance detector means for receiving said output signals and to supply no detector output signal when said output signals are low in magnitude and full detector output signals when both said output signals are high in magnitude and one detector output signal when only one said output signal is high in magnitude, a plurality of ratio detector means for each direction of traffic, fixed and variable voltage divider means respectively connecting each ratio detector means with said balance detector means, each said variable voltage divider means being independently adjustable and normally adjusted in steps, a plurality of local offset selector means each ineluding a plurality of independent selector control means adjustable for a plurality of offsets, and circuit means connecting said ratio detector means with said independent selector control means at each of said local selector means.

5. In a traffic cycle offset selector control apparatus for controlling allocation of traffic cycle offset for a roadway having inbound and outbound traffic lanes, means for providing signals representative of a characteristic of traffic in each of two opposing directions on said roadway, balance detector means responsive to said characteristic signals to determine which characteristic signal is representative of the greater characteristic of traffic, reference ratio means, ratio detector means coupled with said balance detector means and said reference ratio means for detecting whether the ratio of one characteristic signal to the other characteristic signal is different than said reference ratio, and trafiic cycle offset control means coupled to and controlled by said ratio detector means for con trolling allocation of a particular traffic cycle offset to one of said directions of trafiic on said roadway.

6. A traffic cycle offset selector control apparatus as in claim 5, second reference ratio means, second ratio detector means coupled to said balance detector means and said second reference ratio means for detecting whether the ratio of the said one characteristic signal to the said other characteristic signal is different than said second reference ratio, and second traffic cycle offset control means coupled to and controlled by said second ratio detector means for allocation of a second particular traffic cycle offset to said one of the directions of traffic on said roadway.

7. A traffic cycle offset selector control apparatus as in claim 5, wherein said reference ratio means is a potential divider circuit interposed between said balance detector means and said ratio detector means.

3. A traffic cycle offset selector control apparatus as in claim 5, wherein said traffic cycle offset control means includes inbound and outbound offset preferential relays controlled by said ratio detector means.

9. In a trafiic control system for a highway divided into inbound and outbound traffic lanes, traffic detector means for detecting traffic in said inbound and outbound lanes, each of said detector means developing an output signal, first traffic characteristic computer means for receiving the output signals of said inbound lane detector means and providing a signal proportional to a characteristic of tramc in said inbound lane, second traffic characteristic computer means for receiving the output signals of said outbound lane detector means and providing a signal proportional to a characteristic of traffic in said outbound lane; and an offset selector control means for receiving the characteristic signals provided by said first and second computer means, means for comparing and selecting the greater of said characteristic signals, first reference ratio means, and traffic cycle offset control means coupled to said reference means and said comparing means for controlling allocation of a first preferential offset to one of said directions of traflic when the ratio of the greater to lesser characteristic signals exceeds said first reference ratio.

10. In a traffic control system as claimed in claim 9, second reference ratio means, and second trafiic cycle offset control means for substituting allocation of a second preferential offset to said one of said directions of traffic when the ratio of the greater to lesser signals exceeds said second reference ratio.

11. A traffic cycle offset selector control apparatus for controlling allocation of traffic cycle offset for a roadway having inbound and outbound traffic lanes, means for providing output signals representative of a characteristic of traffic in each of two opposing directions on said roadway, reference ratio means, means for comparing said output signals and applying one of said signals to said reference ratio means to multiply said one signal by said reference ratio, second means for comparing said mutiplied one signal to the other cycle offset, and. traffic signal control means coupled to and controlled by said second comparing means for controlling allocation of a particular traffic cycle offset to one of the directions of traflic on said roadway.

12. In a traffic cycle offset selector control apparatus for controlling allocation of traffic cycle offset for a roadway having inbound and outbound traffic lanes;

means for providing output signals representative of a characteristic of traffic in each of two opposing directions on said roadway;

means for comparing and selecting one of said output signals;

second comparing means;

reference ratio means for applying said selected one signal to said second comparing means, said second comparing means comparing said selected signal to the other signal; and,

traffic cycle offset control means coupled to and controlled by said second comparing means for controlling allocation of a particular traffic cycle offset to one of said directions of traflic on said roadway.

13. Apparatus for controlling the traffic cycle offset relationship to be allocated to inbound and outbound directions of trafi'ic on a multi-lane roadway and comprising:

means for generating an electrical signal characteristic of traflic in said inbound and outbound directions; means coupled to said generating means and having first and second outputs carrying first and second electrical signals thereon with magnitudes respectively 20 representative of said characteristics of traific in said two opposing directions, one of said outputs carryin g the greater of said first and second signals;

reference ratio means;

means for electrically comparing a given ratio of the magnitudes of said first and second signals with said reference ratio, said comparing means developing a third electrical signal when said given ratio is different from said reference ratio; and,

tratfic cycle offset control means coupled to said comparing means and responsive to said third signal for controlling allocation of a particular trafiic cycle offset to one of the directions of traffic on said roadway.

References Cited by the Examiner UNITED STATES PATENTS 2,542,978 2/1951 Barker 340-35 20 THOMAS B. HABECKER, Acting Primary Examiner. 

1. IN A TRAFFIC CONTROL SYSTEM FOR USE ALONG A THROUGHFARE HAVING INBOUND AND OUTBOUND LANES AND TRAFFIC ACTUABLE DETECTOR MEANS FOR DETECTING TRAFFIC IN EACH SAID LANE, COMPRISING TRAFFIC DENSITY COMPUTING MEANS FOR DEVELOPING OUTPUT SIGNALS REPRESENTATIVE OF THE MAGNITUDE OF TRAFIC DENSITY IN EACH SAID LANE, BALANCE DETECTOR MEANS FOR DEATERMINING THE OUTPUT SIGNALS OF GREATER AND LESSER MAGNITUDE AND DEVELOPING A PAIR OF FIRST SWITCHING SIGNALS IN ACCORDANCE THEREWITH, A PLURALITY OF RATIO DECTOR MEANS EACH FOR DETERMINING THE RATIO OF THE MAGNITUDES OF SAID OUTPUT SIGNALS AND DEVELOPING A SECOND SWITCHING SIGNAL WHEN SAID RATION IS GREATER THAN A PREDETERMINED RATIO, FIRST SWILTCHING MEANS CONNECTING SAID COMPUTING MEANS TO SAID RATIO DETECTOR MEANS AND RESPONSIVE TO SAID FIRST SWITCHING SIGNALS ABOVE A PREDETERMINED VALUE TO ACTUATE AT LEAST ONE OF SAID RATIO DETECTOR MEANS A PLURALITY OF PREFERENTIAL OFFSET CONTROL CIRCUITS, AND SECOND SWITCHING MEANS CONNECTED TO EACH SAID RATIO DETECTOR MEANS AND TO ONE OF SAID SECOND SWITCHING SIGNAL TO CUITS AND RESPONSIVE TO SAID SECOND SWITCHING SIGNAL TO CONNECT SAID ONE PREFERENTIAL OFFSET CONTROL CIRCUIT WITH A VOLTAGE SOURCE FOR ENERGIZING SAME. 